1. Field of the Invention
The present invention relates to gas injecting gadgets for producing DRAM semiconductor devices and to a chemical composition therefor. More particularly, the present invention relates to gas injecting gadgets for semiconductor production facilities, endurable to the inferior conditions within the facilities, such as high frequency in high electric field and noxious gas, whereby the production yield of semiconductor memory devices can be improved, and to a chemical composition therefor. Also, the present invention is concerned with a method for producing the gadgets.
2. Description of the Prior Art
To produce a semiconductor device, various techniques and processes have been developed and are now usefully applied. For operating such processes, several or many apparatuses or equipments are necessary. For example, a wafer etching process for DRAM semiconductor device requires essential gas injecting gadgets, such as a cathode, a gas distribution plate (GDP) and a uni-lid GDP. Besides, in manufacturing a DRAM semiconductor device, a shower head, a kind of a gas injecting gadget, is used for a chemical vapor deposition process and a wafer-mounting susceptor is also employed.
The above-illustrated apparatuses play pivotal roles in fabricating the memory DRAM and in determining its data. Until recent, they have been made mainly of aluminum. A typically used aluminum is 6061-T6, which shows a tensile strength of 30 kg/mm.sup.2, an yield strength of 25 kg/mm.sup.2, a draw ratio of 10%, a melting point of 582-652.degree. C. and a hardness of 25-40 Hv. Besides such aluminum, other metals, such as iron, silica, copper, manganese, magnesium, chrome and titanium, are added at trace amounts for manufacturing a gas injecting gadget useful for semiconductor production facilities and a susceptor to be amounted on a wafer.
These conventional gas infecting gadget and susceptor, which are made mainly of such aluminum as has the above physical properties, however, has a significant disadvantage of being susceptible to the high frequency resulting from the strong electric field present in semiconductor production facilities and to noxious gas such as chlorine (Cl.sub.2), hydrogen bromide (HBr) and trifluoronitrogen (NF.sub.3). A certain time after the gadget and the susceptor work in the production facilities, they become to corrode or show deteriorated mechanical properties, being unable to exhibit perfect functions.
Conventionally, to solve this problem, an aluminum material is subjected to precise surface processing and the refined surface is coated with an oxide film, thereby conferring durability to the aluminum for a certain period. That is, the aluminum is reacted with oxygen by carrying out electrolysis in a 7-10% sulfuric acid solution, to form a strong oxide film consisting of Al.sub.2 O.sub.3 at the aluminum's surface. The oxide film serves to protect the aluminum, constituting the gas injecting gadget and the susceptor, from the bad conditions in the semiconductor production facilities, so as to improve the durability of the gadget and the susceptor. During the oxidation reaction, the number of the aluminum oxide coating increases exponentially. After completion of the reaction, there are a large number of pores in the coating and a barrier layer 2-3 .mu.m thick at the aluminum surface. Indeed, it is the barrier layer which protects the aluminum surface. This protecting layer may be reinforced by sealing the pores, that is, filling the pores with nickel salts or other corrosion-resistant or abrasion-resistant materials.
Such aluminum-based materials are molded and processed into the gas injecting gadgets which are durable to the extremely severe conditions within semiconductor production facilities, conventionally by the following method.
First, for example, 6061 aluminum raw material is subjected to an annealing process, then, to a rough cutting process and finally, a precise cutting process, to give a basic shape of the desired gas injecting gadget. Subsequently, a Jet, the core part of the gas injecting gadget, is formed. For this, more than 1,000 holes with a diameter of 1 mm are formed on the aluminum by using a drill after which the aluminum is abraded with a non-ionic material to remove the impurities present on the surface of the aluminum material. The aluminum material thus ready is provided with an oxide coating at its surface by the oxidative reaction which results from the electrolysis of a sulfuric acid solution. After the pores occurring the coating are sealed with nickel salt and the like, a precise cutting process is carried out again, to produce a whole gas injecting be gadget.
To produce a gas injecting gadget with such conventional materials in the above-mentioned method is easy. However, the gas injecting gadget obtained is inferior in corrosion resistance to such gas as fluorine (F.sub.2) or chlorine (Cl.sub.2) as well as in durability to such physical condition as high frequency. Since the surface states of the gas injecting gadget, for instance, hardness, gloss, crack, chromaticity and roughness, are greatly affected by the conditions upon the surface treatment for forming the oxide coating, such as current, voltage, density, composition of chemical solution and temperature, the conditions should be maintained properly. After the surface treatment, the gas injecting gadget is available only for a short time, for instance, 30-90 hours when being mounted in semiconductor production facilities. Especially, hazardous gas penetrates into the barrier layer of the oxide coating and finally damages the whole coating. As a result, the oxide coating breaks down into pieces which, then, fall down on a wafer, resulting in a significant decrease in wafer quality. In addition, as the chemical reactions produced by the reaction between the gas within the facilities and the coating accumulate inside several thousands fine gas injecting holes, each with a diameter of 1 mm, they are considerably reduced in diameter, lowering the amount of gas injected. Thus, there is difficulty in data control that the gas amount to be introduced into the gas injecting gadget should be controlled again in order to constantly maintain the gas amount to be injected upon a wafer.